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Eating Healthy During the Week but Junk-Binging on Weekends is Awful for Gut Health

It's basically just as bad as a consistent diet of junk food, according to a new study.

Let’s admit it — lots of us see the weekend as the time to relax and unwind from our healthy work routines, and this likely involves some junk food (and high-calorie booze). Scientists call this “yo-yo eating,” which means yo-yoing between a healthy diet during the week and binging on junk food over the weekend.

Now, a new study published in the journal Molecular Nutrition and Food Research has some bad news: yo-yo dieting is likely to be just as bad for gut health as a consistent diet of junk. In the first study of its kind, the researchers compared how continuous or irregular exposure to an unhealthy diet can influence gut microbiota — the microbe population living in our intestines.

It’s said that up to 100 trillion microbial cells live in our gut, and these cells influence our metabolism, nutrition, immune function, and even our mental health. An unhealthy gut microbiota has been linked to conditions like obesity and inflammatory bowel disease, so it’s important to keep our gut health intact.

To test out the impact that junk food has on our gut, the researchers split rats into three groups — one only ate low-fat food, one only ate high-fat food, and one group, the “cycled rats,” ate a low-fat diet for four days followed by a high-fat binge for three days. The high-fat junk diet consisted of foods like cake, chips, cookies, meat pies, dim sim (an Australian dumpling inspired by dim sum), and the scientists tracked the changes in the gut microbiota over 16 weeks.

By the end of the study, the cycled rats had gained less weight than the rats who only ate junk food, but they were still 18 percent heavier than the rats who stayed on a full-time healthy diet. The cycled rats consumed 30 percent more energy than the healthy rats despite eating much less food while on the healthy phase of their week. The measurements of their key metabolic functions were somewhere between those of the healthy rats and those of the junk food rats.

However, the gut biota profiles of the cycled rats and the rats who ate only junk food were almost indistinguishable — any exposure to junk food had a significant impact on the gut. Further, the scientists found that junk food diets reduced the microbes that had the ability to metabolize flavonoids, which have been linked to helping with weight loss and stimulating protective functions within the brain.

Although this study was performed on rats, the researchers say that, if the same phenomenon happens with humans, all of the good work from sustaining a healthy diet during the week might be “undone” by binging on junk over the weekend.

However, research has shown that the gut biota profile can change relatively quickly, so it’s not like your gut health is permanently damaged if you’re a weekend junk-binger. Making healthy changes to both diet and lifestyle can improve intestinal health — unprocessed foods, avoiding alcohol, and getting adequate exercise are key, according to the researchers.

Abstaining from any junk food at all for seven days a week may be easier said than done, but the impact on gut health might end up making it worth your while.